Depends on where you intend to go after HAV. You are correct, IB and LA are the only oneworld carriers operating at HAV but there are plenty of options to continue onwards to many points in the Caribbean and the Americas. Some of the closer destinations with scheduled non-stop service include CUN (also MX) as you mentioned, Cayman (KX), Jamaica (JM), Aruba (VH) to name a few.

You may also want to check www.taca.com as well as www.copaair.com for additional regional flights should you decide to re-join your RTW in another country.